As a method for treating waste water, a biological treatment method, a combustion treatment method, a wet oxidization treatment method, or the like have been conventionally widely used. These methods are those for decomposing organic or inorganic chemical substances contained in waste water to make them non-toxic thereby reducing their adverse influence on the environment.
In the biological treatment method, the decomposition of substances to be oxidized is generally time-consuming, and the substances that can be treated are limited to those of low concentration. Therefore, when waste water is at high concentration, it should be diluted to a suitable concentration, thus an extensive area of facilities for treatment is disadvantageously demanded. In addition, byproducts such as excessive sludge are generated, and thus the treatment thereof is often problematic.
In the combustion treatment method, fossil fuel is often used as fuel, resulting in a problem in waste of the resource.
On the other hand, the wet oxidization treatment method for cleaning waste water in liquid phase is excellent without the problems described above. In catalyst-free wet oxidization treatment, however, it is necessary that the reaction be conducted at high temperatures under high pressure and the reaction time be prolonged, thus often necessitating an enlarged device and increasing the operation cost.
As a means of increasing the reaction rate and moderating the reaction conditions, a catalytic wet oxidation treatment method using solid catalyst is proposed. For example, a treatment method using a composite catalyst is described in Japanese Unexamined Patent Publication No. SHO 63-158189, to achieve certain results. However, the conventional catalyst comprising noble metal combined with metal oxide such as titanium oxide often requires high-temperature conditions for achieving efficient treatment and high-pressure conditions for maintaining a liquid phase at such high temperatures, thus suffering from problems such as a higher cost of facilities. When used in combination with an oxidizing agent such as ozone or hydrogen peroxide, the treatment may be made feasible at normal pressures, but is not preferable because of a higher cost of the oxidizing agent.
Japanese Unexamined Patent Publication No. HEI 11-179378 discloses a method for decomposing oxygen-containing organic compound, which can be carried out at a temperature of 100° C. or less. However, the compound to be treated by this prior art method is limited to oxygen-containing compounds having one carbon atom, and in consideration of actual application to waste water from factories and the like, its treatment performance is not satisfactory.
As described above, the wet oxidization treatment method using catalyst is the most excellent to treat waste water, but when efficient treatment is to be realized regardless of the concentration of waste water, there is a problem of inevitably higher costs of facilities, treatment itself and the like.
In view of this, the problem to be solved by the present invention is to provide a technique by which organic and inorganic substances contained in waste water can be treated at high degrees regardless of the concentration and at relatively low temperatures, and thus a device to put the invention into practice can be made compact without requiring large and high-pressure facilities, thus enabling treatment of waste water at low costs.